What do you think, is really a crop sensor better than full frame for macro photography?
Owning the ff 6d and the crop 60d I do think the latter is better for macro for various reasons, this is my practical experience and I'll keep around the 60d if even for macro alone.
1. Working distance on 100mm lens: If using artificial light or taking shots of something tiny that tends to fly, crawl or jump away this focal length on ff is rather short, I guess that's why they also offer a 180mm... or you put a tc on the lens, but the Kenko has issues with the newer camera's afma and lowers iq a bit.
2. Swivel screen, though that wasn't the question: Only the 60d/70d/Rebels have it, it's invaluable for tripod macro work, esp. when paired with Magic Lantern's focus peaking.
3. Last not least dof (you mentioned it): If you do focus stacking you'll use the lens' best aperture setting before diffraction is an issue, which means many more shots required on ff. If using handheld, a deeper dof = smaller aperture means higher iso, i.e. the iso advantage of ff diminishes.
What might not have been mentioned yet: With ff, you are more likely to run into the macro zone where the usable aperture drops, or the problem is more severe, so that even more (over-)compensates for the iso advantage of ff... the only redeeming fact is that you can better noise-reduce recent ff shots than crop, but still higher iso = less dr. All of the above us for usual firefly to butterfly shooting distances, not for extreme 1:1 which I seldom really require.
With a good lens like the 100L and the current crop resolution, the iq of the lens on crop is about the same as on ff... but of course ff shots have more postprocessing elasticity if you need that.
Speaking of AF, I sometimes wish Canon did trap focus. I wonder if ML has that feature?
Yes, it does - move the camera until the phase af point detects af lock, then the camera automatically takes the picture. Very handy if you slowly move the lens forward with a fixed focus setting.